The invention relates to a method for generating electrocutaneous stimulation patterns (i.e., electric stimulation patterns which are perceptible on the skin) as carriers of acoustic information and apparatus for carrying out this method. The apparatus is particularly suited for providing the deaf (i.e., those which are hearing-impaired to a high degree) with signals which bring about sensory patterns on the skin surface which can be interpreted by the wearer as acoustic; e.g. speech information (cf. e.g. U.S. Pat. No. 2,703,344).
In the case of known hearing prostheses, in which above-cited methods are employed, the acoustic signal to be transmitted is separated by means of band-pass filters into a series of k different component signals. The latter are then modulated onto a carrier signal with a frequency of f.sub.T, which lies higher than that of the signals to be transmitted. The k modulation signals thus obtained control currents which are to be supplied to k electrodes which are applied at k locations of the skin surface of the wearer of the apparatus, for example, a deaf patient.
The thus generatable chronologically and locally varying sensory patterns then provide characteristic sensory patterns for individual speech sounds, sound combinations and words. After a certain practice time, the patient can correlate therefrom the learned pattern progressions with acoustic e.g. speech events. In this manner he can differentiate spoken words. The possibility is thus provided of the patient acquiring a vocabulary for this "language" consisting of electrocutaneous signals. The prothesis can then be employed as an independently operating substitute for hearing in instances of speech communication in which a reading-off from the mouth of the speech partner ("lip reading") must be dispensed with (e.g. during telephoning or radio reception). Like apparatus for the transmission of mechanical oscillations (vibrations), it can also be employed for the purpose of reinforcing (or supporting) observation as well as for the purpose of facilitating during speech learning. However, the known apparatus have nevertheless not found widespread use in practice, which is probably based on a series of shortcomings with regard to the psychophysical conditions during electric stimulation of the skin and the correlation of the resulting sensations with speech signals.